The present invention relates to a hot steam generator and, more particularly, to a hot steam generating apparatus especially but not solely for use in steam cooking. The present invention also relates to a water boiler, a vessel for a water boiler and/or steam generator as well as a gas burner for a water boiler or hot steam generating apparatus.
A continuous supply of hot steam is essential for the provision of many services in hotels, restaurants, hospitals and other public or private establishments. Hot steam supply for the afore-mentioned purposes is generally produced by boiling water under atmospheric pressure by directly heating a water vessel. Gas is probably one of the cleanest fluid and is therefore widely use for generating hot steam for the afore-mentioned purposes. In conventional hot steam generating apparatuses using gas burners, a gas burner is placed underneath the bottom of a water vessel. Water contained in the water vessel is heated by direct heating of the bottom of the water vessel by the flames and heat generated by fuel gas combustion. In a conventional burner, the flames are pushed by gas pressure towards the bottom of the water vessel and spread over the bottom surface of the vessel, thereby healing the bottom surface of the vessel. However, conventional gas water heaters of the afore-mentioned type are known to have very low thermal efficiency due to dissipation of the heat from the vessel into the atmosphere and also because the flame contact area only represents a small percentage of the gas combustion area. Typically, the thermal efficiency for conventional water heater or steam generator is below 40% for a large-size gas burner or for a heated water vessel with a flat vessel bottom. Also, the prolonged localized direct spot heating on the bottom of the vessel always causes localized damage to the vessel.
To improve the thermal efficiency of a water boiler or hot steam generator, it has been found in practice that, by arranging a gas burner at one side of the water vessel and the fuel gas outlet at the other side, the hot fuel gases from the burner tend to spread across the whole bottom of the water vessel and provides an even and efficient heating of the water vessel. In U.S. Pat. No. 5,524,608, it has been suggested to include flue pipes which extend across the water vessel and are submerged in the water being boiled for steam generation. Such a proposed arrangement, while providing improved thermal efficiency, is still not optimal for a large-size water boiler or steam generator. Hence, it will be desirable to provide an improved water heater and steam generator with improved thermal efficiency which is suitable for general purposes.
It is therefore an object of the present invention to provide a water boiler or hot steam generator which alleviates the shortcomings of existing water boilers or hot steam generators with an aim to achieving high thermal efficiency and clean combustion, As reliability and low-maintenance costs are important for such applications, it is desirable that such apparatuses have relatively simple designs and can be manufactured at low costs. It is also an object of the present invention to provide an improved gas burner for use with such a water boiler or hot steam generator. It is at least an object of the present invention to provide the general public with alternative choices of water boilers, hot steam generators or gas burners which are simple and at the same time environmental friendly with improved thermal efficiency. Preferably such apparatus should also be provided with improved safety devices.
According to the present invention, there is provided a water boiler or hot steam generator including a gas burner and a water vessel having a peripheral wall, said water vessel includes a combustible gas inlet and an exhaust gas outlet disposed on said peripheral wall of said water vessel, said gas inlet and said gas outlet are interconnected by a flue pipe which is adapted to be fully submerged in the water inside the water vessel during normal operation, wherein combustion of the gas originating from said gas burner occurs almost entirely within said flue pipe and combustion occurs substantially along the length of said flue pipe.
According to a second aspect of the present invention, there is provided a water vessel for water boiling or hot steam generation including a peripheral wall, said water vessel includes a combustible gas inlet and an exhaust gas outlet disposed on said peripheral wall of said water vessel, said gas inlet and said gas outlet are interconnected by a flue pipe which is adapted to be fully submerged in the water inside the water vessel during normal operation, wherein a portion of the flue pipe adjacent to the gas inlet is elevated from the bottom of said water vessel so that, during operation, the space between that portion of said flue pipe and the bottom of said water vessel is filled with water.
Preferably, the path of said flue pipe is convoluted and preferably, said flue pipe includes at least an obtuse bend.
Preferably, the periphery of said flue pipe is surrounded by water in the water vessel during normal operations.
Preferably, an aperture means for abruptly changing the aperture of said flue pipe for a very short length is disposed at a short distance from said gas inlet.
According to a third aspect of the present invention, there is provided a gas burner having a flame outlet with an aperture which is partitioned into 3 parts, the relative area of said 3 parts are adjustable to provide a main flame outlet and secondary flame outlets.